Применение метода контрольных возмущений для определения характерных узлов присоединения комплексной нагрузки при расчетах динамической устойчивости

Рассматривается влияние способа замещения комплексной нагрузки на характер электромеханических переходных процессов в электрических системах (ЭС) от действия больших возмущений. Показано, что установить общие рекомендации относительно способа замещения нагрузки в сложных ЭС затруднительно. Предлагается для опреде­ления характерных узлов нагрузки, оказывающих существенное влияние на характер динамического перехода, применять известный метод контрольных возмущений. Приводятся результаты сравнительных расчетов с использованием предлагаемой методики

Spiders do not escape reproductive manipulations by Wolbachia

<p>Abstract</p> <p>Background</p> <p>Maternally inherited bacteria that reside obligatorily or facultatively in arthropods can increase their prevalence in the population by altering their hosts' reproduction. Such reproductive manipulations have been reported from the major arthropod groups such as insects (in particular hymenopterans, butterflies, dipterans and beetles), crustaceans (isopods) and mites. Despite the observation that endosymbiont bacteria are frequently encountered in spiders and that the sex ratio of particular spider species is strongly female biased, a direct relationship between bacterial infection and sex ratio variation has not yet been demonstrated for this arthropod order.</p> <p>Results</p> <p>Females of the dwarf spider <it>Oedothorax gibbosus </it>exhibit considerable variation in the sex ratio of their clutches and were infected with at least three different endosymbiont bacteria capable of altering host reproduction i.e. <it>Wolbachia</it>, <it>Rickettsia </it>and <it>Cardinium</it>. Breeding experiments show that sex ratio variation in this species is primarily maternally inherited and that removal of the bacteria by antibiotics restores an unbiased sex ratio. Moreover, clutches of females infected with <it>Wolbachia </it>were significantly female biased while uninfected females showed an even sex ratio. As female biased clutches were of significantly smaller size compared to non-distorted clutches, killing of male embryos appears to be the most likely manipulative effect.</p> <p>Conclusions</p> <p>This represents to our knowledge the first direct evidence that endosymbiont bacteria, and in particular <it>Wolbachia</it>, might induce sex ratio variation in spiders. These findings are pivotal to further understand the diversity of reproductive phenotypes observed in this arthropod order.</p

Volatile organic compounds in the Scheldt estuary along the trajectory Antwerp-Vlissingen: Concentration profiles, modelling and estimation of emissions into the atmosphere

During a two years sampling campaign, water samples were taken in the Scheldt estuary between Antwerp and Vlissingen over a 94 km trajectory in order to measure concentrations of 13 volatile chlorinated C-1- and C-2-hydrocarbons and monocyclic aromatic hydrocarbons. Averaged concentrations proved to be in the 8 (CCl4) to 189 ng.l(-1) (tetrachloroethylene) range (n = 72). Concentrations were compared to other estuarine concentration data and to marine concentration data of the adjacent southern North Sea. The increasing concentration profiles towards Antwerp for a number of chlorinated compounds was explained by inputs at and/or upstream of Antwerp. Dilution with marine water and water to air transfer downstream of Antwerp are considered as the main factors which contribute to the decrease in concentration towards open sea. In a second part, modelling and estimation of the water to air exchange transfer was carried out based on the water column concentrations, atmospheric concentration data and available air/water exchange models. Calculated volatilization rates were between 0.1 (CCl4) and 8.6 tonnes.year(-1) (CHCl3). The significance of the amounts emitted was demonstrated by comparison with available data on anthropogenic emissions into surface waters